libxslt build itself an older 0.8.15 version in order to build the 1.1.26 one (possible, but still rare case and that's a big versions difference)
libxslt config script found an older 0.8.15 on the system and mistake with the one you're trying to build, you should check libexslt.so* presence on the system for that 0.8.15 version laying someone.